Numerous progressive lenses are known in the prior art. Progressive lenses have heretofore been designed on the basis that they have distance, near and intermediate viewing zones. The intermediate zone joins the near and distance zones in a cosmetically acceptable way, in the sense that no discontinuities in the lens should be visible to people observing the lens of the wearer. The design of the intermediate zone is based on a line called the “eye path” along which the optical power of the lens increases more or less uniformly.
Prior art progressive lenses attempt to optimise the whole lens surface using the global optimisation criteria, be they surface or ray-traced (optical) quantities that are being optimised. This approach does not take into account that the progressive lens has two functionally distinct areas: those for the foveal vision at far, intermediate and near object distances, and others for the peripheral vision only. Also, the question of the appropriate balance between the sizes of zones intended for clear distance and near vision respectively has, not been addressed to date.
Clinical trials and practitioner surveys suggest that most progressive lenses on the market today exhibit a substantial bias towards the distance vision performance at the expense of near vision. In addition, little attention has been paid to the optics of the zone for intermediate vision.
In addition, the question of optical binocularity has been addressed in prior art progressive lenses only with respect to near vision and dealt with primarily with the choice of the inset of the near reference point (NRP).